#1. Brock Lesnar - ending The Undertaker's record WrestleMania streak

While this doesn't count as "breaking" a record, it certainly counts as ending one. And this was no ordinary record. This was the greatest record in WrestleMania history and one of the greatest streaks in professional wrestling history.
The Undertaker was 21-0 and the streak had become a part of his iconic legacy. However, in one of his more underwhelming WrestleMania bouts, the living legend would fall for the first time at the grandest stage of them all, getting pinned by Brock Lesnar.
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It was one of the most shocking moments in WWE history and will likely remain the most shocking one in WrestleMania history. Many questioned the decision to end the streak, but Vince McMahon justified it as The Undertaker wanting to "give back".
To translate it as straightforward as possible, the reason why the streak was ended was to build Lesnar up as the unbeatable monster that he was - leading to his first WWE Championship reign in over 10 years.
Vince McMahon went out of his way to end the streak to help establish Roman Reigns as the face of WWE. That didn't work out as he would have wanted it to.